The primary objective of this trial is to evaluate the safety & efficacy of aminoguanidine in preserving renal function in patients with insulin dependent diabetes mellitus & overt diabetic nephropathy. Secondary; 1)to evaluate the effect of aminoguanidine on protein crosslinking in diabetic pts as measured by circulating blood and urinary concentrations of advanced glycated endproducts (AGEs),2) to evaluate the relationship between plasma aminoguanidine concentrations and primary and secondary efficacy endpoints as well as adverse events